SPRING EQUINOX: Bill Steffen's weekend forecast: March 20-22

Today we welcome spring! (Astronomical spring). Today is the spring or vernal equinox.

“Equinox” means “equal night” and on the vernal and autumnal equinoxes, there is equal day and night over the entire Earth. Now, if you see the sunrise and sunset for today (7:47 a.m. and 7:54 p.m. for Grand Rapids), you’ll note that the day is not exactly 12 hours. It’s 12 hours and 7 minutes.

There’s two reasons for that. First, we don’t measure sunrise and sunset from the middle of the sun. Sunrise is when the top tip of the sun first appears over a totally flat horizon. Sunset is when the last or top tip of the sun disappears over a totally flat horizon. The second reason is that light bends a little when it enters the Earth’s atmosphere.

From March 11-24, daylight increases the fastest, at 2 minutes and 56 seconds each day. This week, we’ll gain 20 minutes and 32 seconds of daylight.

The spring equinox can occur on March 19, 20 or 21. It’s usually on the 20th.

The last time the March equinox was on March 21 (in UTC — Universal Time Coordinate — in the military is may be referred to as “Zulu” was in 2007. It will happen again in 2101.

Due to time zone differences, the equinox may occur a day earlier at locations that are behind UTC (four hours ahead of EDT). Take the example of the mainland of the United States. While locations following UTC saw a March 21 equinox in 2003 and 2007, there will be no March 21 equinox in the mainland U.S. in the 21st century!

Between 2020 and 2048, March 19 equinoxes will happen every leap year in Central, Pacific, and Mountain time zones in the United States. In the same period, the years between the leap years will see a March 20 equinox.

Weekend forecast

• Friday will be breezy with showers in the morning and tapering off by midday. Gusts of 20-25 mph are possible. The high temperature will be 48 degrees, with a low of 29 degrees.
• Saturday will be dry with intermittent clouds and a high of 51 degrees and a low of 39 degrees.
• Sunday will see a return of rain showers in the morning, with a high of 45 degrees and a low of 28 degrees.

— Check out Bill Steffen's Substack channel.